ASTM D2268 Test Method for Analysis of High-Purity n-Heptane and Isooctane by Capillary Gas Chromatography
2. Summary of Test Method
2.1 The sample is injected into a capillary gas chromatographic column consisting of at least 61 m (200 ft) of stainless steel tubing (0.25-mm (0.010-in.) inside diameter), the inner walls of which are coated with a thin film of stationary liquid. An inert gas transports the sample through the column, in which it is partitioned into its individual components. As each component is eluted from the column, it is detected with a hydrogen flame ionization detector and recorded on a conventional strip-chart recording potentiometer. The detector response from each impurity is then compared with that of a known quantity of an internal standard. After determining the total impurity concentration, the n-heptane, or isooctane purity is obtained by difference.
3. Significance and Use
3.1 This test method is used for specification analysis of high-purity n-heptane and isooctane, which are used as ASTM Knock Test Reference Fuels. Hydrocarbon impurities or contaminants, which can adversely affect the octane number of these fuels, are precisely determined by this method.
